Field of the Invention
The present invention relates to a mirroring device including two storage devices to which an upper limit is set for the number of rewrites of data and a control method of the mirroring device, and a storage medium.
Description of the Related Art
As SSDs (Solid State Drive) come into widespread use, the SSDs have been installed in image formation devices, as auxiliary storage devices. As compared with conventional auxiliary storage devices, the SSDs have advantages in access time, heat generation, operation noise, shock-resistant performance, power consumption, size, and the like, but have disadvantage in that the number of rewrites of data has an upper limit.
As devices relating to such auxiliary storage devices, mirroring devices having a fault tolerance that is improved based on the fact that a probability of simultaneous break of two storage disks is low, are known.
Now, when two SSDs are applied to a mirroring device to improve a fault tolerance, the two SSDs reach the lifetimes thereof at almost the same time based on the number of rewrites of data because writing the same data in the two SSDs is repeated.
Therefore, when two SSDs are applied to a mirroring device, the fault tolerance of the mirroring device is not improved although a mirroring configuration is implemented, which is problematic.
To cope with this problem, there has been proposed a technique in which, when data is to be written in one of SSDs, dummy data is added to the data to cause a difference between the number of rewritable times of data in the two SSDs, which prevents the two SSDs from reaching the lifetimes thereof at almost the same time (e.g., refer to Japanese Laid-Open Patent Publication (Kokai) No. 2013-77283).
However, in the technique of Japanese Laid-Open Patent Publication (Kokai) No. 2013-77283, since dummy data is repeatedly stored in only one of the SSDs, the dummy data stored in an accumulating manner causes the one SSD to reach the lifetime early.
That is, the problem with a mirroring device including two SSDs is that it is impossible to improve the fault tolerance thereof while preventing one of the SSDs from reaching the lifetime thereof early.